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Department of Botany, National Museum of Nature and Science, Amakubo 4-1-1, Tsukuba, Ibaraki 305-0005, Japan
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ABSTRACT |
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Polysphondylium multicystogenum, a new heterothallic species of dictyostelids, is described based on three isolates collected from soils in Sierra Leone, West Africa. This species is characterized by sorophores with a combination of clavate base and ovoid to oblong tip cell, smaller spores and abundant microcyst production under the usual culture conditions for sorocarp formation at 20 C. This is the first report of Polysphondylium producing such abundant microcysts.
Key words: dictyostelid cellular slime molds, mating, microcyst, Polysphondylium multicystogenum, species complex, taxonomy
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSTAXONOMYRESULTS AND DISCUSSIONLITERATURE CITED |
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). This complex includes P. pallidum Olive and similar species, such as P. album Olive. We have examined the mating relationships to identify more clearly the known and unknown species of the P. pallidum complex. We recently discovered two mating groups in soils from Sierra Leone, West Africa. One group was identified as P. pallidum and the other group, considered an unknown taxon (Kawakami and Hagiwara 2008). In the present paper we describe in detail this group as a new species and discuss its unique feature (i.e. abundant microcyst production under the usual culture conditions for sorocarp formation at 20 C). |
MATERIALS AND METHODS |
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). One isolate, AS24, had the same morphology as that of the above three isolates but did not produce macrocysts with them. Therefore the dimensions of the sorocarps of AS24 were not used in the description of this new species.
Morphological observation and terminology.— –
The procedures for morphological observation were according to Hagiwara (1989) and Kawakami and Hagiwara (2002). The isolates were subcultured with Escherichia coli as food on nonnutrient agar plates to which a granular type of activated charcoal was added at 20 or 25 C under 12:12 h light:dark conditions.
Morphological terminology was defined according to those described by Hagiwara (1989). The terms "tip cell" and "whorl index" were defined by Kawakami and Hagiwara (2002, 2008); the tip cell represents the terminal cell of a sorophore tip, and the whorl index indicates the ratio of the number of whorls with four or more branches to the total number of whorls examined and is usually calculated using 40 whorls per isolate.
Mating test.— –
The mating tests were performed according to the procedures described by Kawakami and Hagiwara (1999, 2008). These strains were used for the mating tests: two opposite mating-type strains, C-95 and C-97 of P. tenuissimum H. Hagiw., and two type strains, OH538 of P. colligatum Vadell et Cavender and OH595 of P. tikaliensis Vadell et Cavender.
Abbreviations.— –
These abbreviations are used according to those described by Hagiwara (1989) and Kawakami and Hagiwara (2008). B: number of branches per whorl; BB(max): width of the branch base at the thickest part (µm); BL: branch length (µm); BT: width of the branch tip at 50 µm below the top (µm); IL: internode length (µm); L/W: mean length/width ratio of spores per isolate; MD: mean size of 20 spores per isolate (µm); SB: width of the sorophore base at 100 µm above the bottom (µm); SB(max): width of the sorophore base at the thickest part (µm); ST: width of the sorophore tip at 50 µm below the top (µm); TC: length of the tip cell (µm); TL: length of the terminal segment that is not lengthened (µm); and WI: whorl index. The measurements of dimensions are given as arithmetic ranges or means ± standard deviation, and the number of observations "n" is indicated in parentheses.
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TAXONOMY |
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, 2
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When cultured on nonnutrient agar with E. coli at 20 C, sorocarps usually solitary (FIGS. 1B, C
) or sometimes clustered, erect or inclined, sometimes prostrate, phototropic, with 1–7(–11) nodes, with 2–5(–8) branches per whorl or often with irregular branches (FIG. 1D). Sorophores colorless, sinuous, mostly 1.3–6.6 mm long, gradually tapering from base to tip, comprising a single tier of cells including or sometimes except base; bases clavate (FIGS. 1E, 2A), often with slime matrix, 12–26 µm diam at the thickest part; tips acuminate (FIGS. 1F, 2B), sometimes with collars, 2.5–7.5 µm diam 50 µm below the top; tip cells ovoid to oblong, or sometimes subulate, navicular or subglobose (FIGS. 1F, 2B), 5.5–22.0 µm long; terminal segments 312–713 µm long; internode segments 251–572 µm long. Branches colorless, 112–359 µm long, gradually tapering from base to tip, comprising a single tier of cells including or sometimes except base; bases clavate (FIG. 2C), 4.5–9.0(–12.5) µm diam at the thickest part; tips acuminate (FIG. 2D), sometimes with collars, 2.5–5.0 µm diam 50 µm below the top. Sori white, globose; terminal sori mostly 72–109 µm diam; lateral sori mostly 35–78 µm diam. Spores hyaline, oblong to elliptical (FIG. 1G), usually 1.6–2.0 times longer than width, mostly 5.0–6.0 x 2.9–3.5 µm, with unconsolidated polar granules and sometimes with irregular granules. Pseudoplasmodia radial or fan-shaped (FIG. 1A), centralized. Microcysts globose to subglobose (FIG. 1H), mostly 4.8–6.7 µm diam. Macrocysts globose to subglobose (FIG. 1I), mostly 15.4–38.5 µm diam except outermost fibrillar cell wall.
B: 3.5 ± 1.1 (n = 120); WI: 0.45–0.50; SB: 12.3 ± 2.8 (n = 49); SB (max): 17.6 ± 3.3 (n = 38); ST: 5.3 ± 1.1 (n = 62); TC: 17.6 ± 3.3 (n = 38); IL: 417 ± 78 (n = 60); TL: 495 ± 96 (n = 26); BB(max): 6.8 ± 1.8 (n = 54); BT: 3.8 ± 0.7 (n = 68); BL: 215 ± 64 (n = 57); L/W: 1.7–1.9; MD: 5.4–5.7 x 3.1–3.3.
Habitat. – Soil of thick growth of palm trees and cultivated fields, Sierra Leone.
Cultures examined. – SIERRA LEONE: Freetown. Soil of a thick growth of palm trees, Nov 1995, AS2 (HOLOTYPE, ATCC); SIERRA LEONE: Freetown. Soils of cultivated fields, Nov 1995, AS21 and AS23.
Etymology. – Latin multicystogenum, referring to its abundant microcyst production.
Commentary. –
This species simultaneously produced abundant microcysts with sorocarps on agar plates under usual culture conditions for sorocarp formation at 20 C (FIG. 1A) but did not produce abundant microcysts at 25 C. On the other hand, although it produced more sorocarps at 25 C than at 20 C, most sorocarps formed at 25 C had irregular branches more luxuriantly.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSTAXONOMYRESULTS AND DISCUSSIONLITERATURE CITED |
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).
P. multicystogenum is also similar to P. album especially in having ovoid to oblong and short tip cells and similar branch length. However this species is different from P. album mainly in terms of having typically clavate and narrower sorophore bases and smaller spores and producing abundant microcysts under the conditions shown above (Kawakami and Hagiwara 2008).
In addition P. multicystogenum resembles P. colligatum, P. tenuissimum and P. tikaliensis especially in terms of having small spores (Hagiwara 1979, Vadell and Cavender 1998). However P. multicystogenum is distinguishable from these three species mainly by a smaller number of nodes and abundant microcyst production.
As a result of mating tests, two opposite mating-type isolates, AS2 and AS21 of P. multicystogenum did not produce macrocysts with the tester strains of P. tenuissimum and each type strain of P. colligatum and P. tikaliensis as well as with the testers of P. pallidum and P. album (Kawakami and Hagiwara 2008). These results suggest the possibility that this species also is biologically distinct from other species.
When Polysphondylium multicystogenum was cultivated with E. coli used as food on nonnutrient agar plates at 20 C, numerous amoebae differentiated into microcysts as well as aggregated to form sorocarps (FIG. 1A). However at 25 C this species did not produce abundant microcysts under the same conditions except temperature. Microcysts are considered to represent a transient resting stage, and dictyostelid cellular slime molds generally tend to produce microcysts under unfavorable or suboptimal conditions (Raper 1984). Therefore culture conditions at 20 C also are considered to be so for the growth of P. multicystogenum.
In Polysphondylium nine of the 17 species are known hitherto to produce microcysts, namely P. album (Kawakami and Hagiwara 2008), P. anisocaule Cavender, Stephenson, Landolt et Vadell (Cavender et al 2002), P. arachnoideum Vadell et Cavender (Vadell and Cavender 2007), P. asymetricum Vadell et Cavender (Vadell and Cavender 1998), P. equisetoides Cavender, Landolt, Stephenson, N. Cavender et Vadell (Cavender et al 2004), P. luridum Kauffman, Cavender et Hohl (Kauffman et al 1988), P. pallidum (Kawakami and Hagiwara 2007), P. pseudocandidum H. Hagiw. (Schaap et al 2006) and P. tenuissimum (Schaap et al 2006). For example Kauffman et al (1988) reported that P. luridum produced only microcysts in complete darkness in the absence of charcoal. On the other hand, in our experience none produced abundant microcysts on agar plates under the 12:12 h light:dark conditions for sorocarp formation at 20 C. This is the first report regarding such abundant microcyst production in genus Polysphondylium.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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1 Corresponding author. E-mail: shkawak{at}yahoo.co.jp
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSTAXONOMYRESULTS AND DISCUSSIONLITERATURE CITED |
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———, Stephenson SL, Landolt JC, Vadell EM. 2002. Dictyostelid cellular slime moulds in the forests of New Zealand. NZ J Bot 40:235–264.
Hagiwara H. 1979. The Acrasiales in Japan V. Bull Nat Sc Mus, Tokyo, Ser B 5:67–72.
———. 1989. The taxonomic study of Japanese dictyostelid cellular slime molds. Tokyo: National Science Museum, Tokyo. 131 p.
Kauffman G, Cavender J, Hohl HR. 1988. Polysphondylium luridum, a new dictyostelid with unique spores. Bot Helv 98:123–131.
Kawakami S, Hagiwara H. 1999. Macrocyst formation in three dictyostelid species, Dictyostelium monochasioides, Polysphondylium candidum, and P. pseudo-candidum. Mycoscience 40:359–361.[CrossRef]
———, ———. 2002. Two mating groups of Polysphondylium pallidum, a dictyostelid cellular slime mold. Mycoscience 43:453–457.[CrossRef]
———, ———. 2008. A taxonomic revision of two dictyostelid species, Polysphondylium pallidum and P. album. Mycologia 100:111–121.
Raper KB. 1984. The dictyostelids. Princeton, New Jersey: Princeton Univ. Press. 453 p.
Schaap P, Winckler T, Nelson M, Alvarez-Curto E, Elgie B, Hagiwara H, Cavender J, Milano-Curto A, Rozen DE, Dingermann T, Mutzel R, Baldauf SL. 2006. Molecular phylogeny and evolution of morphology in the social amoebas. Science 314:661–663.
Vadell EM, Cavender JC. 1998. Polysphondylium from forest soils of Tikal, Guatemala. Mycologia 90:715–725.[CrossRef]
———, ———. 2007. Dictyostelids living in the soils of the Atlantic Forest, Iguazú region, Misiones, Argentina: description of new species. Mycologia 99:112–124.
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